[libc-commits] [libc] 5d59385 - [libc] Setup TLS in x86_64 loader.
Siva Chandra Reddy via libc-commits
libc-commits at lists.llvm.org
Fri Aug 7 23:19:16 PDT 2020
Author: Siva Chandra Reddy
Date: 2020-08-07T23:19:03-07:00
New Revision: 5d59385ba67ec20dc4a3e13b9a7088ace970df4d
URL: https://github.com/llvm/llvm-project/commit/5d59385ba67ec20dc4a3e13b9a7088ace970df4d
DIFF: https://github.com/llvm/llvm-project/commit/5d59385ba67ec20dc4a3e13b9a7088ace970df4d.diff
LOG: [libc] Setup TLS in x86_64 loader.
The new code added is still very x86_64 specific. AArch64 support will
be added very soon and refactoring of the loader code will be done as
part of the patches adding it.
Reviewed By: asteinhauser
Differential Revision: https://reviews.llvm.org/D82700
Added:
libc/config/linux/app.h
libc/test/loader/linux/tls_test.cpp
Modified:
libc/config/linux/CMakeLists.txt
libc/loader/linux/x86_64/CMakeLists.txt
libc/loader/linux/x86_64/start.cpp
libc/test/loader/CMakeLists.txt
libc/test/loader/linux/CMakeLists.txt
Removed:
################################################################################
diff --git a/libc/config/linux/CMakeLists.txt b/libc/config/linux/CMakeLists.txt
index c8f496bf3f07..50e98379cf53 100644
--- a/libc/config/linux/CMakeLists.txt
+++ b/libc/config/linux/CMakeLists.txt
@@ -9,3 +9,9 @@ add_gen_header(
DEPENDS
libc.src.__support.common
)
+
+add_header(
+ app_h
+ HDR
+ app.h
+)
diff --git a/libc/config/linux/app.h b/libc/config/linux/app.h
new file mode 100644
index 000000000000..48e42ae2c80a
--- /dev/null
+++ b/libc/config/linux/app.h
@@ -0,0 +1,44 @@
+//===-- Classes to capture properites of linux applications -----*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_CONFIG_LINUX_APP_H
+#define LLVM_LIBC_CONFIG_LINUX_APP_H
+
+#include <stdint.h>
+
+namespace __llvm_libc {
+
+// Data structure to capture properties of the linux/ELF TLS.
+struct TLS {
+ // The load address of the TLS.
+ uintptr_t address;
+
+ // The bytes size of the TLS.
+ uintptr_t size;
+
+ // The alignment of the TLS layout. It assumed that the alignment
+ // value is a power of 2.
+ uintptr_t align;
+};
+
+// Data structure which captures properties of a linux application.
+struct AppProperties {
+ // Page size used for the application.
+ uintptr_t pageSize;
+
+ // The properties of an application's TLS.
+ TLS tls;
+};
+
+// Creates and initializes the TLS area for the current thread. Should not
+// be called before app.tls has been initialized.
+void initTLS();
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_CONFIG_LINUX_APP_H
diff --git a/libc/loader/linux/x86_64/CMakeLists.txt b/libc/loader/linux/x86_64/CMakeLists.txt
index aa118167a06a..ceaa94ee11a3 100644
--- a/libc/loader/linux/x86_64/CMakeLists.txt
+++ b/libc/loader/linux/x86_64/CMakeLists.txt
@@ -4,7 +4,10 @@ add_loader_object(
start.cpp
DEPENDS
libc.config.linux.linux_syscall_h
+ libc.config.linux.app_h
libc.include.sys_syscall
+ libc.src.string.memcpy
+ libc.src.sys.mman.mmap
COMPILE_OPTIONS
-fno-omit-frame-pointer
-ffreestanding # To avoid compiler warnings about calling the main function.
diff --git a/libc/loader/linux/x86_64/start.cpp b/libc/loader/linux/x86_64/start.cpp
index dbd0b367bfc6..320fda96105b 100644
--- a/libc/loader/linux/x86_64/start.cpp
+++ b/libc/loader/linux/x86_64/start.cpp
@@ -6,14 +6,76 @@
//
//===----------------------------------------------------------------------===//
+#include "config/linux/app.h"
#include "config/linux/syscall.h"
+#include "include/sys/mman.h"
#include "include/sys/syscall.h"
+#include "src/string/memcpy.h"
+#include "src/sys/mman/mmap.h"
+#include <asm/prctl.h>
#include <linux/auxvec.h>
+#include <linux/elf.h>
#include <stdint.h>
extern "C" int main(int, char **, char **);
+namespace __llvm_libc {
+
+#ifdef SYS_mmap2
+static constexpr long mmapSyscallNumber = SYS_mmap2;
+#elif SYS_mmap
+static constexpr long mmapSyscallNumber = SYS_mmap;
+#else
+#error "Target platform does not have SYS_mmap or SYS_mmap2 defined"
+#endif
+
+// TODO: Declare var an extern var in config/linux/app.h so that other
+// libc functions can make use of the application wide information. For
+// example, mmap can pick up the page size from here.
+AppProperties app;
+
+// TODO: The function is x86_64 specific. Move it to config/linux/app.h
+// and generalize it. Also, dynamic loading is not handled currently.
+void initTLS() {
+ if (app.tls.size == 0)
+ return;
+
+ // We will assume the alignment is always a power of two.
+ uintptr_t tlsSize = (app.tls.size + app.tls.align) & -app.tls.align;
+
+ // Per the x86_64 TLS ABI, the entry pointed to by the thread pointer is the
+ // address of the TLS block. So, we add more size to accomodate this address
+ // entry.
+ size_t tlsSizeWithAddr = tlsSize + sizeof(uintptr_t);
+
+ // We cannot call the mmap function here as the functions set errno on
+ // failure. Since errno is implemented via a thread local variable, we cannot
+ // use errno before TLS is setup.
+ long mmapRetVal = __llvm_libc::syscall(
+ mmapSyscallNumber, nullptr, tlsSizeWithAddr, PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+ // We cannot check the return value with MAP_FAILED as that is the return
+ // of the mmap function and not the mmap syscall.
+ if (mmapRetVal < 0 && static_cast<uintptr_t>(mmapRetVal) > -app.pageSize)
+ __llvm_libc::syscall(SYS_exit, 1);
+ uintptr_t *tlsAddr = reinterpret_cast<uintptr_t *>(mmapRetVal);
+
+ // x86_64 TLS faces down from the thread pointer with the first entry
+ // pointing to the address of the first real TLS byte.
+ uintptr_t endPtr = reinterpret_cast<uintptr_t>(tlsAddr) + tlsSize;
+ *reinterpret_cast<uintptr_t *>(endPtr) = endPtr;
+
+ __llvm_libc::memcpy(tlsAddr, reinterpret_cast<const void *>(app.tls.address),
+ app.tls.size);
+ if (__llvm_libc::syscall(SYS_arch_prctl, ARCH_SET_FS, endPtr) == -1)
+ __llvm_libc::syscall(SYS_exit, 1);
+}
+
+} // namespace __llvm_libc
+
+using __llvm_libc::app;
+
struct Args {
// At the language level, argc is an int. But we use uint64_t as the x86_64
// ABI specifies it as an 8 byte value.
@@ -53,12 +115,37 @@ extern "C" void _start() {
// After the env array, is the aux-vector. The end of the aux-vector is
// denoted by an AT_NULL entry.
+ Elf64_Phdr *programHdrTable = nullptr;
+ uintptr_t programHdrCount;
for (AuxEntry *aux_entry = reinterpret_cast<AuxEntry *>(env_end_marker + 1);
aux_entry->type != AT_NULL; ++aux_entry) {
- // TODO: Read the aux vector and store necessary information in a libc wide
- // data structure.
+ switch (aux_entry->type) {
+ case AT_PHDR:
+ programHdrTable = reinterpret_cast<Elf64_Phdr *>(aux_entry->value);
+ break;
+ case AT_PHNUM:
+ programHdrCount = aux_entry->value;
+ break;
+ case AT_PAGESZ:
+ app.pageSize = aux_entry->value;
+ break;
+ default:
+ break; // TODO: Read other useful entries from the aux vector.
+ }
}
+ for (uintptr_t i = 0; i < programHdrCount; ++i) {
+ Elf64_Phdr *phdr = programHdrTable + i;
+ if (phdr->p_type != PT_TLS)
+ continue;
+ // TODO: p_vaddr value has to be adjusted for static-pie executables.
+ app.tls.address = phdr->p_vaddr;
+ app.tls.size = phdr->p_memsz;
+ app.tls.align = phdr->p_align;
+ }
+
+ __llvm_libc::initTLS();
+
__llvm_libc::syscall(SYS_exit,
main(args->argc, reinterpret_cast<char **>(args->argv),
reinterpret_cast<char **>(env_ptr)));
diff --git a/libc/test/loader/CMakeLists.txt b/libc/test/loader/CMakeLists.txt
index a38d3884ded6..5123bed8aaa9 100644
--- a/libc/test/loader/CMakeLists.txt
+++ b/libc/test/loader/CMakeLists.txt
@@ -37,9 +37,12 @@ function(add_loader_test target_name)
${LIBC_BUILD_DIR}/include
)
- get_fq_deps_list(fq_deps_list ${ADD_LOADER_TEST_DEPENDS})
- get_object_files_for_test(link_object_files has_skipped_entrypoint_list ${fq_deps_list})
- target_link_libraries(${fq_target_name} ${link_object_files})
+ if(ADD_LOADER_TEST_DEPENDS)
+ get_fq_deps_list(fq_deps_list ${ADD_LOADER_TEST_DEPENDS})
+ add_dependencies(${fq_target_name} ${fq_deps_list})
+ get_object_files_for_test(link_object_files has_skipped_entrypoint_list ${fq_deps_list})
+ target_link_libraries(${fq_target_name} ${link_object_files})
+ endif()
target_link_options(
${fq_target_name}
diff --git a/libc/test/loader/linux/CMakeLists.txt b/libc/test/loader/linux/CMakeLists.txt
index 1f47b2ce3f06..b7899fa4c5c1 100644
--- a/libc/test/loader/linux/CMakeLists.txt
+++ b/libc/test/loader/linux/CMakeLists.txt
@@ -35,3 +35,17 @@ add_loader_test(
DEPENDS
libc.loader.linux.crt1
)
+
+add_loader_test(
+ loader_tls_test
+ SRC
+ tls_test.cpp
+ DEPENDS
+ libc.config.linux.app_h
+ libc.include.errno
+ libc.include.sys_mman
+ libc.loader.linux.crt1
+ libc.src.assert.__assert_fail
+ libc.src.errno.__errno_location
+ libc.src.sys.mman.mmap
+)
diff --git a/libc/test/loader/linux/tls_test.cpp b/libc/test/loader/linux/tls_test.cpp
new file mode 100644
index 000000000000..144d894a2caf
--- /dev/null
+++ b/libc/test/loader/linux/tls_test.cpp
@@ -0,0 +1,40 @@
+//===-- Loader test to check if tls size is read correctly ----------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "include/errno.h"
+#include "include/sys/mman.h"
+
+#undef NDEBUG
+#include "src/assert/assert.h"
+
+#include "src/errno/llvmlibc_errno.h"
+#include "src/sys/mman/mmap.h"
+
+constexpr int threadLocalDataSize = 101;
+_Thread_local int a[threadLocalDataSize] = {123};
+
+int main(int argc, char **argv, char **envp) {
+ assert(a[0] == 123);
+
+ for (int i = 1; i < threadLocalDataSize; ++i)
+ a[i] = i;
+ for (int i = 1; i < threadLocalDataSize; ++i)
+ assert(a[i] == i);
+
+ // Call mmap with bad params so that an error value is
+ // set in errno. Since errno is implemented using a thread
+ // local var, this helps us test setting of errno and
+ // reading it back.
+ assert(llvmlibc_errno == 0);
+ void *addr = __llvm_libc::mmap(nullptr, 0, PROT_READ,
+ MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+ assert(addr == MAP_FAILED);
+ assert(llvmlibc_errno == EINVAL);
+
+ return 0;
+}
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